Method of forming thin-walled metal tubing



Feb. 26, 1963 METHOD OF FORMING THIN-WALLED METAL TUBING Filed March 5, 1958 2 Sheets-Sheet 1 ATTORNEYS H. A. FROMSON 3,078,567

Feb. 26, 1963 H. A. FRoMsoN 3,078,567

METHOD OF FORMING THIN-WALLED METAL TUBING Filed March 5, 1958 2 Sheets-Sheet 2 4 III tinned States Patent fiwg b'l Patented Feb. 26, 1953 ice 3,078,567 METHQED 3F FQRMENG THltN-WALLED METAL TUBING Howard A. Frornson, Rogues Ridge Road, Weston, Conn. Filed Mar. 5, 1958, Ser. No. 719,236 Claims. (ill. Z9--5 t4) The present invention relates to a method of forming thin-walled tubing and relates, more particularly, to a method of forming thin-walled metal tubing in one piece and long lengths.

Au obiect of the invention is the formation of such tubes by a cheap and efficient method with maximum efficiency in the use of the metal.

A further object of the invention is the production of thin-walled tubing by combining extrusion techniques which enable hollow shapes to be formed easily, with rolling techniques which provide a maximum of efiiciency in reducing the thickness of the extruded shapes.

Further objects will become apparent from the following description and by reference to the accompanying drawings. The figures are schematic in the sense that they are not to scale, it being deemed of more importance to illustrate the principles involved than dimensional details. in the accompanying drawings:

FIG. 1 is a perspective view of an extruded tubular member;

P16. 2 is a perspective View of the tubular member shown in PEG. 1 after it has been collapsed;

FIG. 3 is a perspective view of the tubular member shown in FIG. 1 after it has been collapsed and rolled into a flat ribboniike form;

FIG. 4 is a perspective view of a thin-walled tube formed from the flat ribbonlike form shown in FIG. 3;

FIG. 5 is an end view showing a collapsed tubular member such as illustrated in FIG. 2 being rolled;

FIG. 6 is a perspective View of an extruded tubular member shaped to provide a fiat member of a substan tially rectangular cross-section when collapsed;

FIG. 7 is an end View showing the tubular member of FIG. 6 collapsed between two rolls.

FIG. 8 is an end view of another form of collapsed tubular member suitable for use in accordance with the present invention.

FIG. 9 is an end View of another form of extruded tubular member suitable for the production of thin-walled seamless tubing in accordance with the present invention;

HQ. 10 is an end view of the tubular member shown in FIG. 9 after being collapsed and partially elongated and reduced in thickness;

FIG. 11 is an end view of the collapsed tubular member of FIG. 10 after elongation and reduction to a desired wall thickness;

R6. 12 is an end view of the member shown in PEG. 11 after expansion.

Accordin to the present invention, use is made of a preformed metal tube 1, as shown in FIG. 1, which may beformed by extrusion or other suitable procedure such as a conventional seamless tube rolling mill.

The tube 1 is formed so that it has a reduced Wall thickness at two diametrically opposite points 2 on its periphery. Preliminarily, the interior of the tube may be treated with a stop-off or resist such as graphite or a heavy lubricating oil to prevent bonding of the opposed interior wall portions of the tube when it is compressed or rolled flat. However, when the tube is formed from metals such as aluminum which have an oxide formed on the surface thereof, it may not be necessary to treat the interior of the tube to prevent bonding of the opposed interior surfaces.

As indicated in FIG. 2, the tube 1 is collapsed in a plane which passes through the two diametrically opposite points of reduced wall thickness. The collapsing of the tube may be accomplished by passing the tube between a. set of conventional compression rolls. The collapsing of the tube in this manner brings the opposing interior surfaces of the tube into contact with each other along a line or fissure 3, the ends of which are located at the points of reduced wall thickness.

After the tube has been collapsed, as shown in FIG. 2, it is then rolled in lengthwise direction parallel to its axis. The rolling elongates the collapsed tube to a ribbonlike strip, as shown in. FIG. 3, and is continued until the thickness of the ribbonlike strip has been reduced to twice the desired wall thickness of the final thin-walled tube or article. Such rolling will not cause appreciable increase in the width of the collapsed tube or in the transverse dimension of the fissure. Thus, when the ribbonlilce strip is erected to tubular shape, the internal diameter thereof will be substantially the same as the internal diameter of the preformed tube.

The ribbonlike strip may be readily erected as onepiece thin-walled tubing, as shown in FIG. 4, by inserting a needle into the fissure between the opposing interior surfaces of the ribbonlike strip and forcing fluid under pressure into the fissure and between the opposing inte rior surfaces while the ends of the strip are held closed.

If the thickness of the strip after reduction is equal to twice the thickness of the preformed tube at the points of reduced wall thickness, the final thin-walled tube will have substantially smooth sides. However, where the thickness of the strip is less than the thickness of the preformed tube at the points of reduced wall thickness, radially extending fins 4 will extend along opposite sides of the thin-walled tubing.

It will be understood that the tubing may be shipped or stored while it is in the form of a ribbonlike strip for erection as desired at the point of use. .The ribbonlike strip may be readily coiled in any desired lengths and it is much easier to handle in this form and less subject to damage than coils of thin-walled tubing.

In order to avoid cracking or tearing of the collapsed tube at its edges as it is rolled to the ribbonlike strip, certain conditions must be observed. One of these conditions is that the opposing interior surfaces of the collapsed tube defining the fissure must be brought into contact with each other and be under compression as indicated by the arrows A in FIG. 5 before the metal at the edges of the tube; i.e., beyond the ends of the fissure, has been elongated beyond the percentage of elongation for the metal from which the preformed tube is made as defined by the standard handbooks. For example, the nominal percentage of elongation for soft temper aluminum in alloy 3003 is 25%.

To insure that the above condition is satisfied, the points of reduced wall thickness 2 for the preformed tube 1 may be calculated as follows:

If e, the percentage of elongation of the metal used is efined by the equation Lil-LI e- LI where L is the initial length of a tensile test specimen and L is the final length of the same tensile test specimen just before fracture, if T is the maximum wall thickness at any point on the preformed tube 1, and if T is the wall thickness at the points 2 of reduced wall thickness, then cracking will not occur as long as The above equation will apply to a great many shapes. As shown in FIG. 1, the preformed tube has a circular outer surface and an elliptical inner surface. However, it

amass? will be understood that other shapes having diametrically opposed points of reduced thickness wiil comply with the above equation, since the distortion incidental to rolling makes the choice of the initial cross-section somewhat arbitrary. As further examples, the inner surface of the preformed tube may be circular and the outer surface may be elliptical. Also, both inner and outer surfaces may be elliptical, and the variations in wall thickness obtained by varying their eccentricity. In addition, the inner and outer surfaces may be in the shape of polygons.

In order to minhnize the width of the fins and still observe the above conditions, a preformed tube 1, as shown in FIG. 6, which is shaped to present a substantially rectangular cross-section when collapsed and before reduction in thickness has taken place, may be employed. FIG. 7 illustrates the preformed tube 1' of PEG. 6 collapsed between rolls, and as can be seen, virtually the whole cross'section of the tube 3. will be under compression, as indicated by the arrows B, from the beginning of elongation. This prevents cracks developing at the edges during elongation and the wall thickness at points 2 of the preformed tube 1 may approximate the desired final wall thickness quite closely.

From actual experience, it has been found that a tubular member of the shape illustrated in FIG. 9 can be formed into thin-walled seamless tubing in accordance with the present invention with a minimum width of fin extending along the sides thereof. In fact, there will only be a small insignificant protuberance 4 extending along each side of the thin-walled tubing which means that maximum elficiency has been achieved in use of the metal in the preformed tubular member.

The preformed tubular member 1 shown in FIG. 9 is extruded from aluminum. The outer transverse surfaces 5 of the tubular member which are substantially fiat join sloping surfaces 6 at their ends which join concave surfaces 7 at the ends of the tubular member.

Transverse surfaces 8 on the inside of the tubular member are also fiat and join sloping surfaces 9 at their ends which intersect at points spaced from the concave outer surfaces at the ends of the member by a distance approxi mately equal to the final desired wall thickness of the thin-walled tubing.

The tubular member 1 as initially formed has a wall thickness between the surfaces 5 and 8 of about 0.1875 of an inch and a wall thickness of about 0.040 at the points 2'.

On one pass through the rolls, the tubular member is collapsed and is partially elongated with its thickness being reduced accordingly as shown in FIG. 10. At this time, the overall thickness of the collapsed tubular member is about 0.140 of an inch, with the distance at points 2 remaining substantially the same.

A second pass through the rolls further elongates the tubular member and reduces its thickness to twice the final desired wall thickness. On this instance its thickness is about 0.080 of an inch as shown in FIG. 11. In this condition the tubular member is in the fiat ribbonlike form described above.

Thereafter the tubular member can be inflated or expanded by internal pressure as and when desired, to give the expanded tube of FIG. 12. This tube has a wall thickness of 0.040 inch.

A similar result is possible if a'preformed tube 1 of uniform wall thickness is collapsed as shown in FIG. 8 and is then trimmed along the lines C-C by means of slitting rolls to leave a thickness of metal, at points 2", between the cut edges of the collapsed tube and the outer ends of the fissure 3 which is at least equal to the desired final wall thickness of the thin-walled tubing. The remainder of the tube is then processed as described above, while the pieces cut therefrom can be reused.

It will be understood that the word arcuately as used herein applies to arched forms such as i of FIG. 9' as A well as those composed of curved segments or segments of circles.

It will be understood that various changes and modifications in the procedure for making thin-walled tubing described above may be made by those skilled in the art without departing from the scope of the invention as defined by the following claims.

I claim:

1. The method of making hollow thin-walled articles which comprises: forming a hollow metal member having points of reduced wall thickness at two opposed points in its periphery, the wall at said points of reduced thick ness being not less than the maximum wall thickness at any point multiplied by the expression where e is the percentage of elongation of the material from which the hollow member is formed; compressing said hollow member and collapsing it on a plane passing through the said opposed points; and rolling said compressed member to a ribbon-like form with unbonded internal opposed surfaces, said rolling elongating and reducing the thickness of said compressed member to twice the desired wall thickness of the final article.

2. The method of making thin-walled tubes which comprises: forming a hollow metal member having a central cavity and substantially constant Wall thickness; compressing the hollow mernbcr and thus collapsing its central cavity into a fissure; trimming the edges of the collapsed hollow member to leave a thickness of metal between the edge of the fissure and the trimmed surface at least as great as the desired final wall thickness; and rolling the compressed hollow member to a ribbon-like form wtih unbonded internal opposed surfaces, said rolling elongated and reducing the thickness of the final.

article.

3. In a method of producing thin-Walled metal tubing, the steps which comprise: extending a hollow metal member having sides defining a central cavity, the sides of said member having a cross-sectional shape comprising two arcuately shaped segments enclosing said central cavity, said segments being of substantially constant thickness and each having concave and convex side portions with the outer ends of the concave side portions of the two segments being joined together at opposite side edges of said member, said concave side portions having a thickness at the point where they are joined less than the thickness of the arcuate segments but not less than the final wall thickness of the thin-walled tubing, applying a weld resisting material to internal surfaces of the hollow member; compressing said hollow member and collapsing it to a flattened condition on a plane passing through the points at which concave side portions are joined, said collapsed hollow member having in cross-section fiat upper and lower surfaces and substantially straight end surfaces extending therebetween; and rolling said collapsed memher in a lengthwise direction between opposing pressure rolls and simultaneously elongating and reducing the thickness of the collapsed member to twice the final wall thickness of the thin-wall tubing.

4. In a method of producing thin-Walled metal tubing as defined in claim 3 wherein the sides defining the central cavity in the hollow member are hexagonal in shape.

5. In a method of producing thin-walled metal tubing, the steps which comprise: extruding a hollow metal mcmher having a central cavity, said hollow member being symmetrical in cross-section about a given plane and including two substantially rectangular portions extending parallel to said plane on opposite sides thereof and four substantially rectangular end portions of the same thickness as the central portions, each of said end portions being joined at one end to one of the central portions and sloping downwardly therefrom toward and joining with another of said end portions at said given plane with the wall thickness where said end portions join being less than the thickness of the central portions but at least equal to the wall thickness of the final thin-walled tubing; the outer edge surfaces -at the points where the end portions join being concave in cross-section; compressing said hollow member and collapsing it in the given plane to a flattened condition; and then rolling the collapsed hollow member in a lengthwise direction and simultaneously elongating and reducing the thickness of the collapsed hollow member to a thickness equal to twice the thickness of the final thin-walled tubing.

References Cited in the file of this patent UNITED STATES PATENTS 185,378 Whitehouse Dec. 12, 1876 6 Marshall Jan. 31, 1888 Davis Nov. 2, 1909 Roesch Oct. 4, 1921 Mantle Aug. 18, 1931 Chase et a1 Mar. 20, 1934 Woods Jan. 27, 1942 Blair Nov. 28, 1944 FOREIGN PATENTS Great Britain AD. 1888 Great Britain AD. 1893 Great Britain Dec. 28, 1922 Great Britain July 10, 1957 

2. THE METHOD OF MAKING THIN-WALLED TUBES WHICH COMPRISES: FORMING A HOLLOW METAL MEMBER HAVING A CENTRAL CAVITY AND SUBSTANTIALLY CONSTANT WALL THICKNESS; COMPRESSING THE HOLLOW MEMBER AND THUS COLLAPSING ITS CENTRAL CAVITY INTO A FISSURE; TRIMMING THE EDGES OF THE COLLAPSED HOLLOW MEMBER TO LEAVE A THICKNESS OF METAL BETWEEN THE EDGE OF THE FISSURE AND THE TRIMMED SURFACE AT LEAST AS GREAT AS THE DESIRED FINAL WALL THICKNESS; AND ROLLING THE COMPRESSED HOLLOW MEMBER TO A RIBBON-LIKE FORM WITH UNBONDED INTERNAL OPPOSED SURFACES, SAID ROLLING ELONGATED AND REDUCING THE THICKNESS OF THE FINAL ARTICLE. 